A power transmission apparatus transmits power from the vehicle engine to the vehicle wheels. The apparatus enables radial, axial and moment displacements caused by the bound of wheels and the turning of the vehicle during travel. The apparatus includes a drive shaft 100 arranged between the engine and the driving wheel. One end of the drive shaft 100 is connected to a differential gear 102 via a slidable constant velocity universal joint 101. The other end of the drive shaft is connected to a wheel 105 via a bearing apparatus 104 which includes a fixed type constant velocity universal joint 103, as shown in FIG. 13.
A prior art bearing apparatus 104 for a vehicle driving wheel is shown in FIG. 11. The apparatus 104 includes a wheel hub 106 for mounting the wheel 105, a double row rolling bearing 107 for rotatably support the wheel hub 106 and a fixed type constant velocity universal joint 103. The universal joint 103 is adapted to be connected to the wheel hub 106 to transmits the power to the wheel hub.
It is known that torsion is created in the drive shaft 100 by a large torque from the engine, via the slidable constant velocity universal joint 101, at a low engine speed, such as during starting movement of a vehicle. As a result, torsion is also created on an inner ring 109 of the double row rolling bearing 107 which supports the driving shaft 100. A stick-slip noise is generated at the abutting surfaces between the outer joint member 108 and the inner ring 109 due to radical slip therebetween when a large amount of torsion exist in the driving shaft 100.
A bearing apparatus for a vehicle driving wheel is known for example from Japanese Laid open publication No. 5404/1999. The bearing apparatus has a wheel hub 110 on which the inner ring 109 is fitted. The inner wheel 109 is axially secured by a caulked portion 111 formed on the inner end portion of the wheel hub 110. The wheel hub 110 and the outer joint member 108 are united by a nut 113. The outer joint member 108 is fitted in the wheel hub 110 via the serration 112. The shoulder of the outer joint member 108 is abutted to the inner end surface of the caulked portion 111.
Accordingly, the pre-load of the double row rolling bearing 107 can be easily controlled and maintained without strongly fastening the nut 113 as in a conventional manner and also without strictly controlling the fastening torque. In addition, the wheel hub 110 and the outer joint member 108 can be united by lightly tightening the nut 113. Therefore it is possible to prevent generation of the stick-slip noise at the abutting surfaces between the inner ring 109 and the outer joint member 108 although the torsion would be caused on the outer joint member 108. However, in such a bearing apparatus for a driving wheel, noise generation or loosening of the nut 113 is sometimes caused during rapid acceleration and deceleration times when circumferential backlash occurs in the fitted portion of the serration 112. In order to resolve this problem, a helix angle is provided in the serration 112 of the outer joint member 108. The serration 112 is press fit into the serration 114 of the wheel hub 110 to eliminate the circumferential backlash in the fitted portion. In such a construction, a problem exists in that a machine, such as a press or the like, is required to assemble or disassemble the wheel hub 110 and the outer joint member 108. This reduces the working efficiency.
While this structure can maintain the pre-load of the rolling bearing 107 lightly tightened to the nut 113, another problem is created. A small gap is created at the abutted portion between the wheel hub 110 and the outer joint member 108. This lowers the sealing performance. If rain water penetrates into the bearing, the serration fitted portion will be rigidly seized by rust, which also reduces the working efficiency.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.